1. Field of the Invention
Aspects of the present invention relate to an apparatus and method for compensating for a phase error in a wireless communication system. More particularly, aspects of the present invention relate to an apparatus and method for compensating for a phase error of a self interference channel or an inter-antenna interference channel in a Relay Station (RS) of a wireless communication system using a Full Duplex Relay (FDR) scheme.
2. Description of the Related Art
In order to provide wireless channels to Mobile Stations (MSs) located in an edge or a shadow area of a cell, wireless communication systems provide relay services. For example, the wireless communication system relays a signal, which is transmitted/received between a Base Station (BS) and an MS, using a Relay Station (RS) as illustrated in FIG. 1 below.
FIG. 1 illustrates a construction of a wireless communication system for providing a relay service according to the related art.
As illustrated in FIG. 1, the wireless communication system includes a BS 100, an RS 110, and MSs 101 and 111.
The BS 100 performs direct communication with the MS1 101 located in a service area, and performs communication with the MS2 111 located out of the service area using the RS 110.
In a case of providing the relay service as above, the RS 110 supports the relay service using a Half Duplex Relay (HDR) scheme or a Full Duplex Relay (FDR) scheme.
In a case of using the HDR scheme, the RS 110 separates channel resources for performing communication with the BS 100 from channel resources for performing communication with the MS2 111, for use. Thus, frequency efficiency is lowered.
In a case of using the FDR scheme, the RS 110 performs communication with the MS2 111 using the same channel resources as channel resources for performing communication with the BS 100. For example, in the case of using the FDR scheme, the RS 110 performs communication with the MS2 111 using the same time resources as time resources for performing communication with the BS 100.
That is, in the case of using the FDR scheme, the RS 110 receives a signal from the BS 100 while transmitting a signal to the MS2 111, or receives a signal from the MS2 111 while transmitting a signal to the BS 100. Thus, a self interference or an inter-antenna interference occurs.
As a result, the RS 110 cannot provide the relay service in the FDR scheme until canceling the self interference or the inter-antenna interference. The RS 110 is aware of a signal, which it transmits. Thus, the RS 110 uses the transmit signal as a pilot to estimate an interference channel functioning as interference of a receive signal. For example, the RS 110 estimates a channel in a unit of burst.
In a case where the wireless communication system providing the relay service uses an OFDM scheme, the RS 110 estimates an interference channel in a unit of burst, and compensates for a phase error based on any one symbol within a burst. Thus, in a case where the RS 110 estimates an interference channel by an average of a plurality of bursts, a problem occurs in that the RS 110 fails to compensate for a phase difference between bursts as illustrated in FIG. 2.
FIGS. 2A and 2B illustrate phase differences between bursts according to the related art.
In more detail, FIG. 2A illustrates a phase before compensating for phase errors of symbols, and FIG. 2B illustrates a phase after compensating for the phase errors of the symbols.
In a case of an OFDM scheme, each symbol constituting a receive signal has a different phase error as illustrated in FIG. 2A.
Thus, as illustrated in FIG. 2B, an RS compensates for a phase error based on any one symbol within each burst.
In a case of an FDR scheme, a transmit signal level of the RS is greater than a receive signal level. Therefore, the RS estimates an interference channel by an average of a plurality of bursts in order to accurately estimate a channel of a transmit signal functioning as interference in a receive signal. In this case, there occurs a problem that the RS cannot estimate an accurate interference channel because a phase error between bursts is different as illustrated in FIG. 2B.
Therefore, a need exists for an apparatus and method for estimating an accurate interference channel by compensating for phase error between bursts in a wireless communication system.